I have a 90 GXL with a bad apex seal, but I plan on rebuilding the engine...in the meantime, I pulled the great running engine out of my 91 coupe and put it in the 90 and now after driving it, the idle surges between 0 and 1000 rpms until it eventually stalls itself out. I am pretty sure everything is hooked up right, but I can not understand how the engine had no problem in the 91, and idles bad in the 90?!? Also, before I pulled the bad engine from the 90, it had no problem with the idle...and we changed the engine from the 91 to the 90 in 7 hours so it didn't sit up for a long time. I believe it should be something simple, only I don't know what to look for...Any help would be greatly appreciated.

 

Have you adjusted the TPS, and checked for any vacuum leaks? A very boucy idle is ofter attributed to a mal-adjusted TPS.

 

I did not touch the TPS during the swap and all vacuum hoses are plugged in. The car runs great while in gear, just when in nuetral and at idle does it become eratic to the point of an eventual stall. Again, the motor ran fine yesterday morning in the 91...and has idled badly since we finished the swap to the 90 last night...

 

bump

 

When you do any sort of engine swapping, you should re-check the timing and TPS. It's a simple thing to do.